Dynamo brush



May 5, 1931. N. R. HAAs 1,804 @52 DYNAMO BRUSH l Filed ot. 10, 1925EFAPH/ TE Patented May 1931 UNITED STATES PArEN'n OFFICE i N'ELSONROBERT HAAS, OF DAYTON, OHIO, ASSIGNOR, BY MESNE ASSIGNNEELNTSQ T0DELCO-BEMY CORPORATION, OF DAYTON, OHIO, A CORPORATION OF DELAWAREDYNAMO :BRUSH Application led October 10, 1925.

This invention relates to commutator brushes for dynamo electricmachines and -particularly to brushes composed of a sintered mixture ofgraphite, a carbonized binder and an abrasive.

It has been known to shape into briquettes,

mixtures of graphite and synthetic resins and to heatthe briquettes in anon-oxidizing at- .mosphere at a temperature sufficient to drive olf thevolatile matter from thel binder so that the particles of graphite willbe held together only by the coked residue of the binder.

One of the objects of the present invention is to produce economically,brushes composed brush in accordance with my invention.

- With these objects in view, the present invention provides for the useof ingredients having a high degree of uniformity as regards theirchemical and physical properties.

While artificial graphite has proved satisfactory, very vgood resultscan be obtained with certain grades of'natural graphite. One such gradeis known to the trade as Dixonls No. .067 4 natural graphite. Thegraphite used should not contain more than 1% ash and should passthrough a 200 mesh screen.

One species of synthetic resin which may be used as a binder Iis aphenol-formaldehyde. resin, one form of which is `lmown to the.

trade as bakelite, grade 2A.

One formula which has roduced a satisfactor brush is 91% graphite and 9%bakelite. n order that the bakelite will be uniformly distributedthroughout the graphite l and thatthe granules of bakelite will be sepasSerial N'o. 61,842.

(82% in the example given) and then the entire mixture is mixed for onehour in a pot mill mixer. Previously computed quantities of thispowdered mixture are pressed in a compound molding die having recessesfor receiving a substantial quantity of briquettes, 40 to 50 forexample. Before introducing the powder, the dies are previously.preheated (preferably by steam) to 250 F4. and then are cleaned oliwith a cloth saturated with a volatile acid, such as stearicl acid; andthe briquette punches and dies are lightly powdered with talcum.

Pressure is applied to the. punch until it enters the die recess apredetermined distance which. is determined by a suitable stop. Providedthe closing distance of the punch with respect to the die is maintaineduniform and uniform quantities of the powder are pressed in the dierecess, the briquetting pressure will be uniform. This pressure shouldbe ap- Kili proximately 3000 pounds per square inch.

This temperature and pressure is maintained .for six minutes, which isknown as the curing time of the compound in the mold. The steam forheating the die is turned 0E and cool water between 60 and 7 0 Fahr; isturned into the die for three minutes while the briquetting pressure isstill maintained. rlhe step of cooling while maintaining pres-l surecauses the set of the briquetted material.

to be more permanent and thus assists in eliminating blisters on thesurface of the briquettes and hence renders the briquettes more uniformin density.

The briquettes are next packed with line charcoal preferably in anichrome carbonizing pot. The briquettes are packed in layers and thelayers are separated by a thin layer of charcoal. A number of these otsare heated for ten hours in a suitable ace at at least 900 F. or at atemperature for a time sucient to convert substantially all of thebakelite into carbon, so that the graphite particles will be boundtogether with particles of coked bakelite. If this is not done thebriquettes will not give satisfaction as a commutator brush. The prsenceof uncarbonized bakelite causes the brush to become soft in use and towear away very rapidly. The

sinteriiig time and temperature specified have I proved satisfactory forbrushes which are thick. Obviously brushes having a greater bakelitecontent or brushes which are thicker require a longer time or greatertemperature to carbonize'all ofthe bakelite.V

After the sintering step the carbonizing pots are removed from thefurnace but the lids are left on and the contents are undisturbed untilthe contents are cooled to roomV temperature. One purpose of this stepisto render brushes less likely to crack or to have surface checks whichare believed to be caused by exposing the brushes while heated, directlyto room temperature. By 7keeping them packed in the carbonizing potsthey are aly lowedto cool olf more gradually.

A modified and preferred form of the present invention results fromsubstituting for vcrushed into sizes which will permit the maximumamountto be pressed'in a carbonizing pot. This scrap is heated inanon-oxidizing l. atmosphere from 6 to 7 hours 'at about 1700 F. whichcauses the bakelite material to be converted into carbon in the formy ofcoke. This carbon is removed from the ot and ground so that it will allpass a 65 mes screen.

vFor 10% of the 91%' graphite used in the preceding example 10% ofbakelite coke is substituted, so that the formula in this examplebecomes 81% graphite, 10% bakelite coke and 9% bakelite grade 2A.' Theseingredients are mixed in the following manner. As stated inthe previousexample, 9% of bakelite and 9% grap ite are mixed in-a'pot mill mixerfor 30 minutes in order that the granules of bakelite shall bethoroughly coated with graphite. To this mixture is added 72% graphiteand 10% lbakelite coke and the total mixture is mixed for one hour in apot mill mixer. The succeeding steps of the process are carried out asstated in the firstexample. The presence of the bakelite coke particlesuniformly distributed in the briquette apparently assist in the escapeof volatile matter during the sintering operation. There is usually lessdistortion or other changing in sha e when coke particles are used.

e present invention is notlimited to the use of natural graphite havingthe desired uniformity of physical andchemical charac- Vteristics'. lAuniform grade` of artificial graphite may be used, but when this is doneit is necessary to add a small quantity of linel divided abrasive suchas levigated alumina. 1y order that the alumina will be uniformlydistributed throughout the mass, the alumina should be mixed withsubstantially an equal ortion of graphite in a pot mill mixer for ateast an hour in order that the granules of alumina will be thorou hlycoated with graplhite. The gran ules o bakeliteare thoroug ly coatedwith graphite by mixin bakelite with an equal amount of grap ite asalready specified. Then these two mixtures are thoroughly mixed togetherwith bakelite coke and with thev balance of the graphite, and thebriquetting and sintering operations are carried out aspreviouslystated.

In all of the examples given it has been specified that the granules ofbakelite should be thoroughly coated Withgraphite before the bakelite ismixed with the balance of th graphite required b the formulae.

What is claimed is as follows:

1. A dynamo brush'in which lthe different ingredients contained in saidbrush are uniformly distributed therethrough and com- 2. A dynamo brushin which the different ingredients contained in saidA brush areuniformly distributed therethrough and comprisinv a sintered mixture ofgraphite, articles of previously coked phenolic-con ensation product anda binder of phenolic-condensation product.

3. The method of making a dynamo brush.

composed of a sintered mixture of graphite and a h drocarbon binderwhich consists first in mixing the binder with a portion onl of thegraphite used in order to coat the particles o thoroughly mixing thismixture with the balance o the graphite, in shapin the mixture,

l d in heating' in a non-oxii phere.

4. Thev methodlof making a dynamo brush which includes briquetting amixture of graphite and a binder under heat and pressure, cooling thebriquette while maintain.- ing the briquetting pressure, and heating'thebriquette in a non-oxidizing atmosphere.

5. The method of making a dynamo brush which includes briquettin in aheated mold a mixture of graphite an a binder, in coolzvi'ng atmosingthe mold and briquette while the briquetting pressure is maintained, andin heating the briquette in a non-'oxidizin atmosphere. 6. The method ofmaking a. ynamo brush which includes briquetting a mixture of graphiteand a binder of synthetic resin in a mold heated to at least 250 Fahr.,in coolin the briquette in theinold to at least 100 while thebriquetting pressure is maintained, and in heating the briquette in anon-oxidizing atmosphere. I,

. The method of ,malng a dynamo brush the binder-with the graphite,then` los' 1h10Q leo l lesI iso

which includes briquetting a mixture of graphite and aphenolic-condensation product-in a mold heated to between 250 and 300Fahr., in cooling the briquette in the mold to at least 100 Fahr., andin heating the briquette in a non-oxidizing atmosphere.

8.v The method of making a dynamo brush which includes brquetting amixture' of graphite and phenolic-condensation product in a mold heatedto'between 250 and 300 Fahr., .the briquetting pressure being about 3000lbs. perpsquare inch and the heat being maintained for about 6 minutes,in cooling the mold to at least 100 Fahr. while maintainving thebriquetting pressure, and in heating the briquette in a non-oxidizingatmosphere.

9. The method of making a dynamo brush which includes briquetting amixture of graphite and phenolic-condensation product in a mold heatedto between 250 and 300 Fahr., the briquetting pressure being about 3000lbs. per square inch and the heat being maintained for about 6 minutes,and in cooling the mold by subjecting itffor about 3 minutes to coolrunning Water While maintaining the briquettingpressure, and in heatingthe briquette in a non-oxidizing atmosphere. y

10. The method of making a dynamo brush comprising graphite and ahydro-carbon binder, which consists in coking a part ot the binder,mixing graphite with the uncoired portion of the binder, then mixing thecoiled portion of said binder with the mixture thus formed, shaping themixture into the desire form and heating said mixture in a nonoxidizingatmospherelJ p 11. The method of making a dynamo brush comprisinggraphite and la hydro-carbon binder, which consists -in coking a part orthe binder, mixing a part of the graphite Twith the uncoked portion ofthe binder, then mixing the coked portion of the binder and re- /mainderlof the graphite with the mixture thus formed, shaping the mixture intothe desired form and heating said mixture in a non-oxidizing atmosphere.f

12. The method oi making a dynamo brush -i comprising graphite and ahydro-carbon binder which consists in coking substantially half of thebinder, mixing the uncoked half of the binder Witha substantially equalquantity of graphite, then mixing the re- .mainder of the graphite andthe coked portion of the binder ,with the mixture thus formed,-shapingthe mixture into the desired form and heatln said mixture lin a nonoxidizingatmosp ere.

` 13. The method of-making a dynamo brush comprising approximately 81%graphite and the coked portion of the Vbinder with the mixture thusformed, shapino' the mixture into the desired form and heating saidmixture in,

vmixture of approximately') parts carbon including graphite andpreviously coked hydrocarbon binder and 1 part uncoked hydr'ocarbonbinder. l

18.. dynamo brush comprising a sintered mixture of approximately 8 partsgraphite, 1 part previously coked hydrocarbon binder, and 1 part uncokedbinder.

19. A dynamo brush comprising a sintered mixture of 81% graphite, 10%previously eek-ed bakelite, and 9% uncoked bakelite. in testimonywhereof hereto ax my signature..

NELSON ROBERT HAAS.

' 19% hydro-carbon binder, which consists in 7,-'

coking approximately one-halt the binder mixing substantially one-ninthof the graphite with the uncoked portion et the binder mixing theremainder of the graph'te and

